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Keywords: Arsênio;  ressuspensão de sedimentos;  óxi-hidróxidos de ferro;  piritização;  estuário.;  Arsenic;  resuspension of sediments;  iron oxyhydroxides;  pyritization;  and estuary.
Issue Date: 13-Jun-2008
Abstract: In order to understand the geochemistry of arsenic at an estuarine environment, this work sought for addressing this issue in different ways grouping varied techniques and methods, such as surface mapping, pyritization degree, datation and interpretations that might assist understanding the possible enrichment of this element. One hypothesis was to verify the influence of anthropic activities, especially concerning the production of fertilizers, to the arsenic sediments concentrations in the Paranguá Esturine Complex, also assessing the geochemistry factors that influence in its mobility and distribution. Besides the arsenic metalloid, the focus of this research, the elements iron and aluminium were analyzed due to their properties as important indicators of geochemistry processes to the understanding arsenic geochemistry behavior. Grain size, organic content, total organic carbon (TOC) and carbonates analysis were also performed. Arsenic concentrations vary from 0,60 to 10,99 mg/kg for the surface sediments samples in the Paranaguá Estuarine System and, specifically in the samples from the main navigation channel of the estuary, the values were up to 21,70 mg/kg. In the sediment cores, arsenic concentrations vary from 2,7 (basis), which were assumed as a reference level for the site, to 8,4 mg/kg (surface). Sedimentation rates estimations, calculated from the decay of 210Pb, were 0,6 cm/ano for the intern region of the estuary and 0,2 cm/year in the median sector. Moreover, in the median sector this value were obtained until around 30 cm of depth and at the deepest layers the sedimentary rate was 1,4 cm/year. Among all investigated variables, iron presents a positive relation with the element arsenic. Considering that 70% of arsenic in the water column are presented as dissolved form, iron is the main geochemistry agent for the mobility and distribution of arsenic, together with hydrodynamic conditions. Highest variations of arsenic concentrations in surface sediments were found close to Paranaguá city, especially in the north margin and at the intern sector of the navigation channel. The north margin of the Paranaguá Estuarine Complex presents significant increases in arsenic concentrations, reaching 17 times over the assumed regional reference level (2,7 mg/kg) calculated by the Enrichment Factor (EF), and 20 times over the reference level calculated from the Geoaccumulation Index (lgeo). Arsenic pyritization trace metal degree (DTMP-As) is intensified at the eutrophic regions and minor in oligotrophic area of the estuarine system. Benito Inlet and Paranaguá (eutrophic) presented higher values of DTMP-As due to pyritization degree (DOP), reaching almost 100% of arsenic pyritization while pyritization degree (DOP) varied from 40 to 75%. At Paranaguá, DTMP-As and DOP values are slightly lower then these values (92% and 40%, respectively), especially in the surface layers (0-2 and 2-5 cm). At the Mel Island (eutrophic) DTMP-As ranged from 3,51% to 13,43%, while DOP was from 17,63% to 37,22%. So the iron element can be consider as dominant factor for the arsenic metalloid, both in surface sediments and in sedimentary column.
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